1. Field of the Invention
The invention is related to an article for use in a dishwashing machine to reduce corrosion of glassware.
2. The Related Art
Corrosion of glassware in cleaning and/or rinsing cycles of an automatic dishwashing machine is a well-known problem. This corrosion problem will create, after a certain number of cleaning cycles, damages on the glassware, such as turbidity, scratches, streaks and the like.
There are different approaches in the prior art proposed for the solution of above identified problems.
One approach is the use of zinc, either in metallic form (U.S. Pat. No. 3,677,820) or in the form of zinc compounds. The use of soluble zinc salts for inhibition of corrosion of glassware in automatic dishwashing processes is, for example, disclosed in U.S. Pat. No. 3,255,117.
Another approach is the use of insoluble zinc compounds for the inhibition of corrosion of glassware in automatic dishwashing processes as described in European Patent Application EP 0 383 480 A1, EP 0 383 482 A1 and EP 0 387 997 A1. More particularly insoluble zinc salts such as zinc silicate, zinc carbonate, zinc oxide, basic zinc carbonate, zinc hydroxide, zinc oxalate, zinc monophosphate and zinc pyrophosphate have been proposed. With these prior art compositions, it is disadvantageous that, due to the low solubility, or even insolubility, of the zinc compounds, it is difficult, if not impossible, to ensure an continuously sufficient amount of active corrosion inhibiting agent in the wash liquor or rinse water.
Patent applications WO 00/39259 A1, WO 01/64823 A1 and pending application GB 0104347 disclose the use of water-soluble glass and ceramic compositions, respectively, as corrosion protection for glassware. These compositions comprise at least one compound, which in cleaning and/or rinsing cycles of a dishwashing machine releases a corrosion-inhibiting agent.
It has been suggested that it may be advantageous to use such water-soluble glass or ceramic materials in the form of a large shaped body, which could be placed into the dishwasher and would allow a prolonged glass protection effect. However, the use of the glass or ceramic compositions in powder or granular form into conventional detergent or rinse compositions is also possible.
However, when actually testing the compositions described in WO 00/39259 a number of problems have become apparent.
A first problem found, in particular when the water-soluble glass or ceramic compositions are in the form of a shaped body, is that the shaped bodies show the undesirable tendency of developing sharp edges on dissolution. This is indeed a big problem for their use by the consumers particularly when large shaped bodies for several cycles are used as there is the potential risk that the consumer is injured when manipulating the contents of the dishwasher (plates, cutlery . . . ) in the vicinity of the region where the partially dissolved shaped bodies having developed sharp edges are to be found.
The applicant has tried to find a solution to the problem of the shaped bodies developing sharp edges by giving the shaped bodies different shapes in the hope to find a shape, which will avoid the development of the “sharp edges”. This route has, however, proven to be not sufficient to fully solve the problem.
A second problem is that, when the shaped body is added to the dishwasher without taking special measures to control its free movement within the machine, it may end up sitting in the bottom of the machine reservoir close to the heating elements of the dishwasher. This will have the undesirable effect of substantially increasing the dissolution rate of the shaped body thereby unnecessarily shortening its lifetime. Alternatively the glass may get stacked in a place within the dishwasher where it is poorly exposed to the washing liquor. This will result in a sub-optimal glass-protecting performance.
Although the above-mentioned disadvantages would be solved by instructing the consumer to place the shaped body in an existing predetermined position of the dishwasher where its capacity to move is restricted, this may also cause problems.
The straightforward point to place the shaped body if one wants to restrict its movement is the cutlery basket.
However, placing the shaped body in the cutlery basket has also a number of disadvantages for the consumer. One clear disadvantage is that it occupies space the consumer would have used to place its cutlery thereby reducing the efficiency of the cleaning process as fewer cutleries per wash can be placed in the dishwasher. Another disadvantage is that once the shaped body is sitting in the cutlery basket, the consumer may drop cutlery in the compartment occupied by the shaped body causing it to break with the risk that the consumer is then injured by the broken glass or that small pieces of glass or ceramic may damage the dishwasher.
Still a third problem of using the glass shaped bodies in the dishwasher arises from the thermal shock they have to face when hot washing liquor is pumped off the machine and new fresh cold water enters the machine in a short time period. This thermal shock may again cause the shaped body to break with the associated problems described above.
A solution for these problems have been proposed in unpublished British Patent Application GB 0107593, the disclosure of which is incorporated herein by reference. The solution described in this patent application is characterized by a kit for use in a dishwashing machine to dispense a water-soluble glass or ceramic composition into the machine over a plurality of dishwashing cycles, comprising (a) a shaped body made of the water-soluble glass or ceramic composition; and (b) a container preferably made of plastic material for holding said shaped body with at least part of its walls having perforations allowing a controlled circulation of the wash liquor into and out of the container.
However, during the use of such kit, formation of a viscous, gelatinous layer on the surface of the shaped body has been observed. This layer may result in adhesion of the shaped body onto the walls of the container, or in the formation of material clogging the perforations in the walls of the container, thus at least partly blocking off the circulation of the wash liquor into and out of the container. This is in particular true with perforations of a size of less than 7 mm which are preferably chosen for safety reasons, i.e. to avoid larger particles to exit from the container into the dishwashing machine.
A further area where there is room for improvement is that of the stability of water-soluble glass or ceramic glassware protecting compositions. It has been observed that these compositions are sensitive to humidity, which can cause changes in the appearance of the compositions during storage. It has also been found that there is a direct relationship between the water-solubility of the composition and its sensitivity to humidity, which make highly soluble compositions more prone to develop undesired appearance changes when exposed to humidity than those occurring with compositions having lower dissolution rates.
It is however desirable to use compositions with a relatively high rate of dissolution in order to guarantee a sufficient release of the glass-protecting composition to the washing liquors. Therefore the need remains to find ways of improving the rate of dissolution of the compositions in the dishwasher without impairing the sensitivity to moisture.
The object of the present invention is to avoid the above-mentioned specific problems and/or to improve the dissolution of the glass or ceramic composition.